1. Field of the Invention
This invention relates to a wheel rim, and more particularly to a lightweight wheel rim used for a bicycle, wheelbarrow, and other such transportation or carrying apparatus.
2. Description of the Related Art
Referring to FIG. 1, a conventional wheel rim 11 is shown to include two spaced-apart annular sidewalls 111 disposed at two opposite sides of a tire 110, an inner connecting wall 112 interconnecting radial inner ends of the sidewalls 111, and an outer connecting wall 113 interconnecting intermediate portions of the sidewalls 111 and spaced apart from the inner connecting wall 112. During assembly, a plurality of locking heads 114 are inserted through a middle portion of the inner connecting wall 112 to engage respectively and threadably radial outer ends of a plurality of spokes 115 so as to fix the wheel rim 11 to a hub (not shown). However, this causes stress to be concentrated at the middle portion of the inner connecting wall 112.
U.S. Pat. No. 6,257,677 discloses an improved wheel rim so as to solve the stress concentration problem. Referring to FIG. 2, the improved wheel rim 12 is shown to include two sidewalls 121 disposed at two opposite sides of a tire 120, two spoke-mounting seats 122 disposed respectively at radial inner ends of the sidewalls 121, a curved inner connecting wall 123 interconnecting the spoke-mounting seats 122, an outer connecting wall 124 interconnecting the sidewalls 121 and adjacent to the tire 120, and a radially extending reinforcing wall 125 interconnecting the inner and outer connecting walls 123, 124. A plurality of locking heads 126 extend through the spoke-mounting seats 122, and engage respectively and threadably a plurality of spokes 127. The spoke-mounting seats 122 are thicker than the sidewalls 121 and the inner connecting wall 123. As such, stress concentration at the inner connecting wall 123 can be prevented. However, the spoke-mounting seats 122 are heavy and therefore increase the total weight of the wheel rim 12.